JP2002519801A - Method and apparatus for determining bit error rate in sample data system - Google Patents

Abstract

Abstract: A system determines a bit error rate in a sample data system having a disk (112) formed of magnetic media and a data head (126) for writing and retrieving data to and from the disk (112). . A pattern is written on the disk (112), which includes an isolated instance (248) associated with a given event. The pattern is retrieved from the disk (112) and the isolated instances (248) are combined to obtain a representative instance s _av (n) with reduced media noise components. The representative instance s _av (n) is combined with each isolated instance (248) to obtain a noise sequence. An autocorrelation component (R) is obtained based on the instance and the noise sequence read from the disk (112). A channel filter with an impulse response is developed based on the requirements for the representative instance and a given channel model. A representative instance is filtered to obtain a filter output (smp), and an error value indicative of a bit error rate is determined based on the filter output samples and the autocorrelation component (R).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001] The present invention relates to a sample data system. In particular, the invention relates to a system for determining the bit error rate of a sampled data system that includes a disk and a data head used to write and retrieve data from the disk.

BACKGROUND OF THE INVENTION A typical disk drive includes one or more magnetic disks mounted for rotation on a hub or spindle. Typical disk drives also include a transducer supported by hydrodynamic air bearings floating over each magnetic disk. The transducer and hydrodynamic air bearing are collectively referred to as a data head. Conventionally, a drive controller is used to control a disk drive based on a command received from a host system. The drive controller controls the disk drive to retrieve information from the magnetic disk and store information on the magnetic disk.

[0003] Electromechanical actuators operate in negative feedback, closed loop servo systems. The actuator moves the data head radially over the disk surface for track seek operations and holds the transducer directly above the tracks on the disk surface for track following operations.

[0004] Information is typically stored in concentric tracks on the surface of the magnetic disk by providing a write signal to the data head to encode a flux reversal on the surface of the magnetic disk that represents the data to be stored. When retrieving data from the disk, the data controller floats on the magnetic disk, senses magnetic flux reversal on the magnetic disk, and the drive controller controls the electromechanical actuator to generate a read signal based on the magnetic flux reversal. . The read signal is typically adjusted and then decoded by the drive controller to recover the data represented by the flux reversal stored on the magnetic disk, and thus represented in the read signal provided by the data head.

[0005] A typical readout system consists of a data head, preconditioning logic (
Preamplifier and filtering circuits, etc.), and data detector and recovery (
recovery) circuitry, and error detection and correction circuitry.
The read system can be implemented as a separate circuit or in a drive controller associated with a disk drive.

In a disk drive, it is important to maintain an error rate (bit error rate) with respect to the number of recording bits at a relatively low level. In a working disk drive, the bit error rate can be estimated in several ways. For example, various data patterns can be continuously read from and written to a disk in a disk drive, and the number of errors encountered during data reading can be easily counted. However, during the development of next generation disk drives, it is rare for a drive manufacturer to test and evaluate several different data heads or different types of data heads before selecting a data head to be implemented in a next generation disk drive. The development of data heads often precedes the development of read channel circuits using these data heads. Therefore, it is difficult to estimate the bit error rate of a system using such a data head unless the read channel circuit is available.

[0007] In the past, attempts have been made to estimate the bit error rate of systems utilizing such heads (where no read channel circuitry is available) by making measurements which are believed to be at least somewhat helpful. Not successful. Typically, such measurements include measuring the signal and noise stored on the disk to the extent that they can be measured. However, such conventional measurements do not correlate well with the bit error rates encountered in utilizing such data heads in disk drive systems.

[0008] The present invention addresses these and other issues, and provides advantages over the prior art.

SUMMARY OF THE INVENTION A system determines a bit error rate in a sampled data system having a disk formed of magnetic media and a data head for writing and retrieving data to and from the disk. A pattern is written on a disk containing M isolated instances associated with a given event. The pattern is retrieved from the disk and the M isolated instances are combined to obtain a representative instance with reduced electronic noise components. A representative instance is combined with each isolated instance to form M
Noise sequences are obtained. An autocorrelation component is obtained based on the M instances and the M noise sequences read from the disk. A channel filter with an impulse response is developed based on the representative instance and the channel requirements for a given channel mode. The representative instance is filtered to obtain a filter output sample, and an error value indicating a bit error rate is determined based on the filter output sample and the autocorrelation component.

The present invention can be implemented as both a method and an apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Determining the bit error rate associated with a data sampling system utilizing a data head without the need for read / write channel circuitry typically associated with a disk drive utilizing a data head Provide a system that can However, for the purpose of a thorough understanding of the present invention, the disk drive and its associated read / write channel circuitry will be described here for clarity.

FIG. 1 diagrammatically illustrates a rotary magnetic disk drive system generally designated 110. A plurality of magnetic information storage disks 112 are journaled about a spindle motor assembly 114 in a housing 116. Each magnetic disk 112 has 118
Has a large number of concentric recording tracks for recording information schematically shown in FIG. Each track 118 is subdivided into a plurality of sectors indicated schematically at 120. Data can be stored or retrieved from disk 112 by referring to specific tracks 118 and sectors 120. Preferably, an actuator arm assembly 122 is rotatably mounted at one corner of the housing 116. The actuator arm assembly 122 carries a plurality of head gimbal assemblies 124 each carrying a slider 125 having a read / write head, or a transducer 126 reading and writing information from and to the magnetic disk 112. Voice coil 128 precisely rotates actuator arm assembly 122 back and forth, and transducer 126 moves magnetic disk 112 along arc 130.
Is to cross.

FIG. 2 shows a high-level block diagram of the control circuit 132 of the disk drive system 110. Disk drive system 110 includes a control circuit 132 that controls the position of transducer 126 and processes information written to or received from disk 112. Microcontroller 134 directly implements all key functions of disk drive system 110. A read / write support and interface control circuit and motor and actuator controller 138, indicated generally at 136, are connected to the microcontroller 134 by a general purpose data, address, and control bus 140. Generally, circuit 136 provides a hardware interface between disk drive system 110 and a host computer system (not shown) via communication bus 142. Also, the circuit 136 generally includes a motor and actuator controller 138.
And an interface between read and write channels 144. Read / write channel 144 acts as an interface between microcontroller 134 and transducer 126 via line 145. Read / write channel 144 also provides signals to motor and actuator controller 138 via line 146. Controller 138 provides an interface between microcontroller 134 and motor assembly 114 via line 148 and an interface between microcontroller 134 and actuator arm assembly 122 via line 150.

Data to be written to the disk 112 is provided to a read / write support interface circuit 136, and then to a read / write channel 144.
The read / write channel 144 passes data to the data head 126, which acts to encode data on the surface of the disk 112.

To read data from the disk 112, the head 126 passes over a track on the surface of the disk 112 where data is to be written and reads a signal indicating a magnetic flux reversal on the track. The read signal is provided from the data head 126 to a read / write channel 144 that typically includes a channel filter and a detector. One common type of channel filter is a finite impulse response (FIR) filter with multiple taps. A common type of detector is a Viterbi-type detector that detects the data according to a trellis structure in a known manner. The filter passes the data to a Viterbi detector where the data is detected. The detected data is typically sent to a decoder where the data is decoded and forwarded for further processing.

When the manufacturer is evaluating a new or different data head 126, the drive manufacturer may not utilize (obtain) the read / write channel circuit 144 used with the new data head. Read / write channel circuit 144
Is typically not fully developed when the data head is being tested and evaluated.

FIG. 3 is a block diagram of a bit error rate measurement system including the head 126 and the disk 112 for measuring the bit error rate of the sample data system. The system shown in FIG. 3 includes a controller 200, a servo controller 202,
Includes data head 126 and disk 112. Controller 200 includes a pattern generator 204 and a bit error rate (BER) element 206. The bit error rate is determined by the head 126 and the medium (ie, disk) 112.
Calculated directly from measurements made using, and no read / write channel electronics are required.

According to the invention, the probability of error for a particular error event can be calculated from the measured values.

The pattern generator 204 generates a pattern associated with a dominant error event (ie, any other desired error event for which a bit error rate is desired). The pattern generator 204 is connected to the head 126 and controls the head 126 to write a pattern on the surface of the disk 112. Servo controller 202
Can be any suitable servo controller, such as the motor and actuator control circuit 138 shown in FIG. The servo controller 202 controls the radial position of the head 126 with respect to the disk 112.

The BER element 206 is directly connected to the head 12 without an associated read / write channel circuit.
6 to search for a pattern written on the disk 112. The raw read signal (after conventional amplification and conditioning) from head 126 is used by BER element 206,
Measure the bit error rate associated with the system.

FIG. 4 shows a first waveform 208 and a second waveform 210. One dominant error event in such a system has been found to be caused by writing a dip pulse, shown as waveform 208 in FIG. That is, anticipating sample +/- (10-1) and reading sample (000) will generate a dominant error event. Thus, although the bit error rate can be measured for any desired error event, the present description is for an error event where a dipulse is written and a constant magnetization is read.

For clarity, a trellis detector is then used to derive a probability equation for the error encountered. Consider the probability of a particular error event in which a decision is made by a trellis, as in the case of a Viterbi detector. Such an error event occurs when the path metric of the incorrect path is smaller than the path metric of the correct path through the trellis. It is assumed that the correct path is the path “a” having the path metric M _a in the merge state. Furthermore, the path having the path metric M _b in incorrect path merge state "b
".

(Equation 1) Here, s _k represents a noisy sample, and a _k and b _k represent noiseless values of path a and path b, respectively. Equation 1 can be rewritten as

(Equation 2) Here, e _k = a _k -b _k and n _k, denotes the noise sample at time k. The sequence [e _k ] is an error event that causes an error. PR4 If the channel is a [e _k] = [10-1] or [-101]. For EPR4 channel is a [e _k] = [11-1-1] or [-1-111].

Of course, other error events can be considered. Wherein the sum of n _k e _k is the very close to Gaussian sum (Gaussian). Thus, a standard Q (or error) function can be used. Therefore, Equation 2 becomes as follows.

(Equation 3)

Equation 3 defines the effective signal-to-noise ratio (ESNR) by:

(Equation 4) In particular, for the PR4 channel,

(Equation 5) For four EPR channels,

(Equation 6)

Now that the equations for the bit error rate have been generally obtained for the PR4 and EPR4 channels in particular, a system for making measurements to obtain bit error rate values will now be described in detail.

FIG. 5 is a flow diagram illustrating the operation of BER element 206 shown in FIG. 3 (block 230-2).
72). FIG. 6 is a more detailed functional block diagram of the BER element 206.

The BER element 206 includes a pattern search element 212, a data storage 214, a pattern alignment and averaging element 216, a representative instance generator 218, a noise sequence generator 220, an autocorrelation matrix generator 222, and a channel filter generator 224. , _Ro generator 226, and BER determining element 228. Substantially all of the functional blocks shown in FIG. 6 can be implemented in a single integrated microprocessor or microcontroller with associated program modules, memory and timing circuits. The operation of BER element 206 will be described with respect to both FIGS.

First, an appropriate pattern starting with an isolated pulse used for signal alignment is written once. A suitable pattern is an isolated dipulse in that the error event is for writing a dipulse and reading out a constant magnetization. The write pattern preferably includes multiple (eg, M) isolated instances that reflect the error event. An example of a pattern written on the surface of the disk 112 is shown in FIG. FIG. 7-1 is a graph of voltage along axis 242 and time along axis 244. An alignment pulse 246 is provided in the first frame of the pattern. Thereafter, a plurality of isolated dipulses 248 are recorded.

Of course, the tripulse in which the error event in question is shifted
If so, M isolated pulses are written to the disk 112.

In one embodiment, the pattern includes 220 isolated instances that reflect error events. The writing of the pattern on the disk 112 is performed by the block 23 in FIG.
0 is shown.

Next, the pattern search element 212 searches the disk 112 for a pattern. In one embodiment, pattern search element 212 includes a conventional amplification and signal conditioning circuit that searches for read signals from data head 126. Next, pattern search element 2
Reference numeral 12 denotes a signal indicating a read signal from the disk drive 112,
Give to 14. The element includes one or more solid state storage devices. Reading and storing the pattern is indicated by block 232 in FIG.

In one embodiment, a bit error rate substantially independent of electronic noise can be obtained. For this purpose, the pattern search circuit 212 reads the pattern a plurality of times (for example, 20 times) and stores each of them in the data storage device 214. It is indicated by block 234 in FIG. The reason for reading the pattern a plurality of times is that the plurality of patterns read from the disk 112 can be averaged to suppress electronic noise associated with the read signal. Therefore, the electronic noise component related to the average pattern is significantly reduced. Of course, as the number of times the pattern is read and averaged increases, the associated electronic noise component decreases. If electronic noise is included in the calculation of the bit error rate, the pattern is read only once from the surface of the disk 112.

In either case, if the pattern is read more than once, each pattern is retrieved from data storage 214 by pattern alignment and averaging element 216. Pattern alignment and averaging element 216 provides alignment signal 246
(In one embodiment, an isolated pulse) is used to properly align all patterns. Next, element 216 averages all patterns to obtain an averaged pattern. If the pattern is read N times and the N patterns are averaged, the electronic noise component associated with the pattern is reduced to 1 / √N. Further, the rotation speed of the spindle support disk 112 varies. Thus, element 216 can adjust the pattern length before averaging to adjust for spindle speed variations. Pattern alignment and averaging are shown in blocks 236, 238 and 240 of FIG.

The pattern written on the disk contains M isolated instances. Once the average pattern is obtained, the M isolated instances in the averaged pattern are separated and temporarily aligned so that they can be averaged to suppress any media noise components associated with the M isolated instances. Is done. FIG. 7-2 is a graph of time along axis 250 and voltage along axis 252. FIG. 7-2 shows a plurality of isolated instances 254 that are aligned for averaging. To average the isolated instances 254, the representative instance generator 254 retrieves the averaging pattern from the data storage 214, separates the pattern into M isolated pulses, aligns the pulses, and averages them. It is indicated by block 256 in FIG. The averaged signal is denoted by s _av (n) with a suppressed medium noise component. Thus, the signal s _av (n) is obtained such that both electronic and medium noise are removed therefrom.

Next, the signal s _av (n) is subtracted from the M isolated (and noisy) instances to obtain M noise sequences. The noise sequence generator 220 retrieves from the data storage 214 both the M noisy isolated noise sequences and the noiseless sequences (included in s _av (n)) and subtracts one from the other. Thereby, M noise sequences are generated and the autocorrelation matrix generator 2
22. It is indicated by block 258 in FIG.

Autocorrelation matrix generator 222 averages M noise sequences over M noisy isolated instances to obtain autocorrelation matrix R. The autocorrelation matrix equation is as follows.

(Equation 7) Where k is assumed to be from 0 to M-1 over M noise sequences. The indices i and j relate to points in a particular noise sequence. The length of the noise sequence is L. The generation of the autocorrelation matrix is indicated by block 260 in FIG.

Next, the channel filter generator 224 generates a channel filter. To that end, the channel filter generator 224 uses the signal s _av (n) as a channel filter input and imposes channel requirements on the channel filter output. Channel requirements desired channel mode selected (i.e., corresponding to the requirements of the channel equalization target (equali zation target). For example, in one embodiment, the channel requirements PR4 channel, EPR4 channel, and E ² PR4 channel The channel filter generator 224 generates a channel filter having an impulse response h (n) based on the channel requirements of the channel filter input and the channel filter output.The length of the impulse response h (n) Again L. It is shown in block 262 of FIG.

Next, _Ro generator 226 generates an autocorrelation matrix at the channel filter output ( _Ro ). Therefore, R _o generator 226 first matrix H generated, it is 2L-1XL matrix (R is LxL matrix). The H matrix is generated from h (n) as follows.

(Equation 8) Here, L is the length of the noise sequence.

The autocorrelation of the noise at the output of the channel filter, which is the Viterbi trellis input, can be calculated from R and H as described above. The autocorrelation matrix of the channel filter output is defined as follows.

(Equation 9) Where E is an expectation operator and n '(i) is a filtered noise sequence.

The filtered noise at the channel filter output is given by:

(Equation 10) Where n (k) is the channel filter input noise sequence and h (n) is the unit sample response of the channel filter. The length of n (k) and h (k) is one. Equation 1
By substituting 0 into Equation 9, the following equation is obtained.

[Equation 11] Where 0 ≦ i ≦ 2L-2,0 ≦ j ≦ 2L-2,0 ≦ k ≦ L-1,0 ≦ l ≦ L-1

Equation 11 can be written in matrix notation as

(Equation 12) Here, for 0≤ (j-1) ≤L-1, H (i, j) = h (j-1) Otherwise, H (i, j) = 0

The formation of H matrix at the channel filter output R _o and autocorrelation matrix generation is shown in block 264 and 266 of FIG.

Next, the signal s _av (n) is passed to a filter having an impulse response h (n). This gives a noise-free sample +/- (smp, 0, -smp) to the channel filter output, where smp represents the sample value. Thus, enough information is available to calculate the bit error rate defined by Equations 5 and 6. In particular, for the PR4 channel, the bit error rate can be calculated by the following equation.

(Equation 13) Where Q is a standard Gaussian q-function. Thus, the bit error rate determination component retrieves the appropriate values of the autocorrelation component at the channel filter output R _o from R _o generator 226, searches the noiseless samples from channel filter 224, calculates the bit error rate 229. It is the blocks 268, 270 of FIG.
And 272. It is done without read / write channel circuitry and without significant approximation.

The present invention contemplates an overall BER that includes BERs corresponding to two or more error events. FIG. 8 is a flowchart showing the calculation of such an overall bit error rate. Initially, a number of patterns are written to disk 112, each pattern having an isolated instance associated with a different error event. It is shown in blocks 274 and 276. The first pattern is selected from a number of patterns and the bit error rate associated with the error event represented by the pattern is determined. It is shown in blocks 278 and 280. The determination of the bit error rate is performed in substantially the same manner as described with reference to FIG. If any patterns remain, they are selected and the bit error rate associated with those patterns is also determined. It is shown in blocks 282 and 284.

After all bit error rates have been calculated, they are weighted according to their superiority over the overall bit error rate. The weighting function is preferably determined empirically. It is indicated at block 286. Next, all weighted bit error rates are added to obtain the overall bit error rate for the various error events considered. It is shown in blocks 288 and 290.

FIG. 9 is a graph of the autocorrelation matrix at the channel filter input. Time is plotted in nanoseconds along axes 300 and 302 and voltage is plotted along axis 304. The transition interval between isolated instances in the pattern is 10 μ inches (254 nm) and axis 304 is in units of volt ² × 10 ⁻⁵ .

FIG. 10 shows the autocorrelation matrix at the filter output (R _o ) plotted on an axis similar to that shown in FIG.

Thus, the present invention does not require the development of read / write channel circuits and can be used to obtain the bit error rate of a data sampling system without making significant approximations. It takes approximately three minutes for all measurements, and it has been found that it can be used to refine the data head structure and compare different types of data heads to realize next generation disk drives.

The present invention can be implemented as a method for determining a bit error rate in a sample data system having a disk 112 formed of a magnetic medium and a data head 126 for writing and retrieving data to and from the disk 112.
The method includes a step 230 of writing a pattern on the disk 112, where the pattern includes M isolated instances 248 associated with a given error event. The method comprises the steps 232 of retrieving a pattern from the disk 112 and M
The method also includes a step 2256 of combining the isolated instances 248 to obtain a representative instance s _av (n) with reduced media noise components. The method also includes combining 258 the representative instance with each of the M isolated instances 248 to obtain M noise sequences, based on the M instances read from disk 112 and the M noise sequences. Step 2 for obtaining a correlation component R
60, obtaining a channel filter having an impulse response h (n) based on the channel requirements for the representative instance and the predetermined channel model 26
2. Obtaining a filter output sample (smp) through a representative instance of a filter having an impulse response h (n) 268, and determining an error value indicating (BER) based on the filter output sample and the autocorrelation component R 270.
Also included.

In one embodiment, the method further includes storing 232 the pattern retrieved from disk 112. The search step further includes searching for patterns from the disk 112 at a plurality of times (step 234) to obtain a plurality of search patterns and combining them (step 238) to obtain a representative search pattern with reduced electronic noise components. Contains.

In an embodiment, step 238 of combining the search patterns further includes temporarily aligning and averaging the search patterns.

The disk 112 can rotate at a certain speed, and temporarily aligning the search pattern includes, in one embodiment, adjusting the speed of the search pattern to adjust speed fluctuations 240. .

Combining M instances 256 further includes, in one embodiment, temporarily aligning and averaging M isolated instances 248 to obtain representative instances 256. In the preferred embodiment, obtaining M noise sequences reduces the representative instance from M instances Step 2
58. Further, obtaining an autocorrelation component further includes averaging M noise sequences over the M isolated instances 248 to obtain an autocorrelation matrix.

Further, a plurality of isolated instances 24, each associated with a different error event
A plurality of patterns, including 8 can be written on the disk 112. An error value indicating the overall bit error rate corresponding to the error event is obtained based on the weighted error value.

The present invention can also be realized as an apparatus. A pattern writing element 204 writes a pattern on the disk 112. The pattern search element 212 searches for a pattern. First coupling element 218 obtains a representative instance and second coupling element 220
Obtains a noise sequence, and an autocorrelation element generator 222 obtains an autocorrelation component R.
A channel filter generator 224 generates a channel filter and outputs the error determinant 2
28 determines an error value 229 indicating a bit error rate based on the filter output samples and the autocorrelation factor. The pattern search element 212, in one embodiment,
The data storage device 214 is also configured to search the disk 112 for a pattern a plurality of times.

While numerous features and advantages of various embodiments of the present invention have been described in the foregoing description, together with details of the structure and function of the various embodiments of the present invention,
This disclosure is illustrative only and it is within the principles of the present invention to vary the details of construction and construction of parts, particularly to the full extent indicated by the broad general meaning of the terms, for which the appended claims are expressed. it can. For example, a particular element may have a particular equalization target and BER while maintaining substantially the same functionality without departing from the scope and spirit of the invention.
Can be changed according to the desired error event.

[Brief description of the drawings]

FIG. 1 is a plan view of a disk drive from which an upper casing has been removed.

FIG. 2 is a high-level block diagram of the disk drive shown in FIG.

FIG. 3 is a block diagram illustrating a system for determining a bit error rate associated with a data head without using read / write channel electronics.

FIG. 4 illustrates a dominant error event.

FIG. 5 is a flowchart showing the operation of the system shown in FIG. 3;

FIG. 6 is a block diagram showing the system shown in FIG. 3 in more detail;

FIG. 7-1 is a diagram showing a pattern of an isolated pulse according to an embodiment of the present invention.

FIG. 7-2 is a diagram showing an operation of the isolated instance shown in FIG. 7-1 to obtain a noiseless sample.

FIG. 8 is a flow diagram illustrating operation of the system shown in FIG. 6 according to another aspect of the invention.

FIG. 9 illustrates an autocorrelation matrix at the filter input in accordance with one aspect of the present invention.

FIG. 10 illustrates an autocorrelation matrix at the filter output according to one aspect of the present invention.

Claims (10)

[Claims] 1. A method for determining a bit error rate in a sample data system having a disk formed by a magnetic recording medium and a data head for writing and retrieving data to and from the disk, the method comprising the steps of: Writing a pattern including an isolated instance related to the error event on the disk; (b) searching for the pattern from the disk; and (c) combining the isolated instance to reduce a medium noise component. Obtaining a representative instance; (d) combining the representative instance with each of the isolated instances to obtain a corresponding number of noise sequences; (e) the isolated instance and the noise read from the disk. Step to obtain autocorrelation component based on sequence (F) obtaining a channel filter having an impulse response based on the representative instance and channel requirements for a predetermined channel model; and (g) filtering the representative instance through a filter having the impulse response. Obtaining an output sample; and (h) determining an error value indicative of a bit error rate based on the filter output sample and the autocorrelation component. 2. The method according to claim 1, wherein said searching step comprises: (b) (i) searching said pattern from said disc a plurality of times to obtain a plurality of search patterns; ii) combining the search patterns to obtain a representative search pattern with reduced electronic noise components. 3. The method of claim 2, wherein the combining step (b) (ii) comprises: (d) (i) temporarily aligning the search pattern; and (d) (ii) Averaging the search patterns. 4. The method of claim 3, wherein the disk rotates at a speed, and the step of temporarily aligning includes adjusting a length of the retrieved pattern to adjust for speed variations. Method. 5. The method of claim 1, wherein said combining step (c) comprises: (c) (i) temporarily aligning said isolated instances; and (c) (ii) combining said isolated instances. Averaging to obtain the representative instance. 6. The method of claim 1, wherein the step (e) of obtaining the autocorrelation component comprises averaging the noise sequence over the isolated instance to obtain an autocorrelation matrix. 7. The method of claim 1, wherein the writing step includes writing a plurality of patterns on the disk, each including a plurality of isolated instances associated with a different error event. 8. The method of claim 7, further comprising repeating steps (b) to (h) for each of said plurality of patterns. 9. The method of claim 8, further comprising: (i) weighting the determined error values to obtain a weighted error value; and (j) determining a weighted error value. Determining an overall error value indicative of an overall bit error rate corresponding to said error event based on said error event. 10. An apparatus for determining a bit error rate in a sample data system having a disk formed by a magnetic recording medium, the apparatus comprising: a pattern on the disk containing an isolated instance associated with a predetermined error event. A pattern writing element arranged on the disk so as to write to the disk; a pattern search element arranged on the disk so as to search for a pattern from the disk; and A first combining element for combining instances to obtain a representative instance with a reduced media noise component; and a corresponding number coupled to the first combining element for combining the representative instance with each of the isolated instances. A second coupling element for obtaining a noise sequence of An autocorrelation component generator connected to the first instance and connected to the first coupling element to generate an autocorrelation component based on the isolated instance and the noise sequence read from the disk; A channel filter generator for generating a channel filter having an impulse response based on channel requirements for a channel mode, wherein the channel is adapted to receive the representative instance and provide filter output samples. An error determining element coupled to the autocorrelation component generator and the channel filter, the error determining element determining an error value indicative of the bit error rate based on the filter output samples and the autocorrelation component.